This is a note to let you know that I've just added the patch titled
serial: stm32: Re-assert RTS/DE GPIO in RS485 mode only if more data are transmitted
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
serial-stm32-re-assert-rts-de-gpio-in-rs485-mode-onl.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 5409cf4b6a2ce96c8703bb5ac849270555db263c
Author: Marek Vasut <marex@xxxxxxx>
Date: Thu Feb 23 05:22:52 2023 +0100
serial: stm32: Re-assert RTS/DE GPIO in RS485 mode only if more data are transmitted
[ Upstream commit c47527cbcc3c50800f34b8c684f29721f75de246 ]
The stm32_usart_transmit_chars() may be called with empty or stopped
transmit queue, and no XON/OFF character pending. This can happen at
the end of transmission, where this last call is used to either handle
the XON/XOFF x_char, or disable TX interrupt if queue is empty or
stopped.
If that occurs, do not assert the RS485 RTS/DE GPIO anymore, as the
GPIO would remain asserted past the end of transmission and that would
block the RS485 bus after the transmission.
Only assert the RS485 RTS/DE GPIO if there is either pending XON/XOFF
x_char, or at least one character in running transmit queue.
Fixes: d7c76716169d ("serial: stm32: Use TC interrupt to deassert GPIO RTS in RS485 mode")
Signed-off-by: Marek Vasut <marex@xxxxxxx>
Link: https://lore.kernel.org/r/20230223042252.95480-2-marex@xxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 0e6ef24419c8e..28edbaf7bb329 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -690,8 +690,9 @@ static void stm32_usart_transmit_chars(struct uart_port *port)
int ret;
if (!stm32_port->hw_flow_control &&
- port->rs485.flags & SER_RS485_ENABLED) {
- stm32_port->txdone = false;
+ port->rs485.flags & SER_RS485_ENABLED &&
+ (port->x_char ||
+ !(uart_circ_empty(xmit) || uart_tx_stopped(port)))) {
stm32_usart_tc_interrupt_disable(port);
stm32_usart_rs485_rts_enable(port);
}
